After several days troubleshooting, I realized these glass syringes are too prone to jamming. @himikestone suggested turning my own plunger (thanks Mike!), so I tried it out and it works great! 303 stainless with #119 viton o-ring. In the video you'll see water pulled up through a check valve, then pushed out through another check valve, creating a one-way system that allows the syringe to measure.